How severe is CVE-2026-42854?

CVE-2026-42854 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2026-42854 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (43rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-42854?

CVE-2026-42854 affects Espressif Arduino-esp32. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-42854?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

Does CVE-2026-42854 have an EU (EUVD) identifier?

Yes. CVE-2026-42854 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-29858.

When was CVE-2026-42854 published?

CVE-2026-42854 was published on 2026-05-12 and last updated on 2026-06-17.

CVE-2026-42854

CVE-2026-42854 is a critical-severity vulnerability in Espressif Arduino-esp32 with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-121.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
EPSS exploit prediction: 1% (43rd percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-29858
Weakness: CWE-121
Affected product: Espressif Arduino-esp32
Published: 2026-05-12
Last modified: 2026-06-17

Description

arduino-esp32 is an Arduino core for the ESP32, ESP32-S2, ESP32-S3, ESP32-C3, ESP32-C6 and ESP32-H2 microcontrollers. Prior to 3.3.8, the WebServer multipart form parser in arduino-esp32 allocates a Variable Length Array (VLA) on the stack whose size is derived from an attacker-controlled HTTP header field (Content-Type: multipart/form-data; boundary=...) without enforcing any length limit. Sending a boundary string longer than ~8000 characters overflows the 8192-byte task stack of the loopTask, causing a crash and potential remote code execution. This vulnerability is fixed in 3.3.8.

Frequently asked questions

What is CVE-2026-42854?: arduino-esp32 is an Arduino core for the ESP32, ESP32-S2, ESP32-S3, ESP32-C3, ESP32-C6 and ESP32-H2 microcontrollers. Prior to 3.3.8, the WebServer multipart form parser in arduino-esp32 allocates a Variable Length Array (VLA) on the stack whose size is derived from an attacker-controlled HTTP header field (Content-Type: multipart/form-data; boundary=...) without enforcing any length limit. Sending a boundary string longer than ~8000 characters overflows the 8192-byte task stack of the loopTask, causing a crash and potential remote code execution. This vulnerability is fixed in 3.3.8.
How severe is CVE-2026-42854?: CVE-2026-42854 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2026-42854 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (43rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-42854?: CVE-2026-42854 affects Espressif Arduino-esp32. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-42854?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
Does CVE-2026-42854 have an EU (EUVD) identifier?: Yes. CVE-2026-42854 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-29858.
When was CVE-2026-42854 published?: CVE-2026-42854 was published on 2026-05-12 and last updated on 2026-06-17.

References

https://github.com/espressif/arduino-esp32/security/advisories/GHSA-8cmm-3887-r32j

Affected products (1)

cpe:2.3:a:espressif:arduino-esp32:*:-:*:*:*:*:*:*

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